1. Field of the Invention
The present invention relates to powered hoists (see DEFINITIONS section) and more particularly to powered hoists for theatrical applications.
2. Description of the Related Art
Hoists are conventional, and the use of powered hoists in theatres to raise, lower and otherwise move lighting and scenery and the like is also conventional. In conventional hoist systems, a widely employed mechanical overspeed brake uses a centrifugal device to detect excessive rotational speed and to deploy linkages to engage a disk or drum brake. This type of brake is sometimes referred to herein as a “mechanical brake.” In a conventional a mechanical brake, the rotational speed that will cause the centrifugal device to deploy its linkages, and brake the rotation, is called the “trigger speed.” The centrifugal device is conventionally designed so that its trigger speed is at or slightly above the “rated speed,” which is the maximum rotational speed at which the hoist travels in normal use. Conventional mechanical brake overspeed protection works well because it allows the lift to perform normal operations, but it will quickly and reliably brake when the rotational speed is too great.
Another type of conventional braking technology is herein referred to as an “electrical brake” because the is controlled by a control signal. As the term “electric brake” is used herein, the electric brake may be fully electric, or, it may be spring applied and electrically released. Generally, electric brakes are controlled by a control signal. In some systems, the control signal is turned on to activate the brake. In other systems, the control signal maintains the brake in a deactivated state, while turning on the control signal will serve to activate the brake. For example, if the electric brake is spring loaded and electrically released, and the system is structured and/or programmed so that turning on the control signal activates the brake, then a total loss of power would be one fault condition that would activate the electric brake. However, many variations are possible. An example of a conventional hoist system 400, with electric brakes, is shown in FIG. 4. As shown in FIG. 4, system 400 includes: load 401; first encoder 402; electric motor 404; reducer 405; motor brake 406 (an electric brake); drum brake 407 (another electric brake); drum assembly 408; cable 409; second encoder 410; first brake controller module 416a; and second brake controller module 416b. The first encoder detects rotation of a rotating portion of the motor and sends a corresponding electrical signal to the first brake controller. The first brake controller uses this signal to determine how fast the motor is rotating and to determine whether an overspeed condition exists in the motor. If there is an overspeed condition in the motor, then the first brake controller sends an electrical control signal to activate the motor brake and thereby slow and stop the hoist. The second encoder detects rotation of a rotating portion of the drum assembly and sends a corresponding electrical signal to the second brake controller. The second brake controller uses this signal to determine how fast the motor is rotating and to determine whether an overspeed condition exists in the drum assembly. If there is an overspeed condition in the drum assembly, then the second brake controller sends an electrical control signal to activate the drum brake to thereby slow and stop the hoist. By using two encoders and two brakes, there is redundancy in the braking sub-system, which is believed to increase reliability and safety.
U.S. Pat. No. 5,996,970 (“Auerbach”) discloses a theatrical rigging system including a counterweight, a motor, a control chain connected to a motor, a brake, a gear box, a cogbelt, scenery, a computer control system and a positioning encoder. The positioning encoder is connected to the cogbelt. The positioning encoder produces an indication of the position of the control chain and thus the scenery. Data output from the positioning encoder is sent to the computer control system. Auerbach states: “The digital encoder provides telemetry control to the master rigging control. The digital encoder is driven by a cogbelt from the output shaft to the gear box. The encoder also has programmed limits. The gear motor is mounted on a self-aligning tensioning base.” (Note: Figure numbers and reference numbers in the preceding quote relate to the Auerbach document and not this document.)
U.S. Pat. No. 6,297,610 (“Bauer”) discloses a system of motor driven winches. The Bauer system includes two types of encoders: (i) the motors each include an encoder or resolver that outputs velocity feedback signals to a VSD 10 through a matrix; and (ii) a position (or velocity) encoder is mounted on the motor shaft so as to provide encoded positional (velocity) signals to an axis controller through the matrix and a termination panel. Bauer further discloses that a satellite module is coupled to monitor the incremental encoder to provide local storage of data relevant to the motor to which it is coupled.
U.S. Pat. No. 7,079,427 (“Power”) discloses an automatic drilling system that includes an electric servo motor operatively coupled to a winch brake drum. Power further discloses that: “A rotary encoder 166 is rotationally coupled to the drum 162. The encoder 166 generates a signal related to the rotational position of the drum 162. Both the servo motor 150 and the encoder 166 are operatively coupled to a controller 168 . . . . The servo motor 150 includes an internal sensor (not shown separately in FIG. 3), which may be a rotary encoder similar to the encoder 166, or other position sensing device, which communicates the rotational position of the servo motor 150 to the controller 168. The encoder 166 in the present embodiment can be a sine/cosine output device coupled to an interpolator (not shown separately) in the controller 168. The encoder 166 in the present embodiment, in cooperation with the interpolator, generates the equivalent of approximately four million output pulses for each complete rotation of the drum 162, thus providing extremely precise indication of the rotational position of the drum 162 at any instant in time . . . . The controller 168 determines, at a selected calculation rate, the rotational speed of the drum 162 by measuring the rate at which pulses from the encoder 166 are detected.” (Note: Figure numbers and reference numbers in the preceding quote relate to the Power document and not this document.)
Description of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).